1. Field of the Invention
This invention relates to material cutting apparatus, such as industrial miter saws, and more particularly, to a measurement and control system for these apparatus which provides accurate cutting of elongated workpieces by actively determining variations in material distal and proximate displacement from a known datum plane and compensating therefor.
2. Description of the Prior Art
Material cutting devices, such as saws, used to cut parts from elongated workpieces are well known. Typically, an elongated workpiece is positioned on a feed table and moved toward a cutting area on the saw by means of a shuttle vise. The shuttle vise engages the elongated workpiece and moves it the desired amount (the “feed length”), and the saw is then used to cut the part. Certain accuracy in the cutting of the parts is necessary, and relatively tight tolerances may be desirable.
When making a “square” cut, one in which the cutting plane is substantially perpendicular to the longitudinal axis of the elongated workpiece, maintaining accuracy is relatively straightforward. Once a part is cut, the material is fed into the saw to the desired dimension, and another cut is made. There are a variety of known devices for maintaining the accuracy of the feeding of the workpiece.
However, when the piece is cut at an angle which is not perpendicular to the axis of the workpiece, referred to as an “angled” cut or “miter” cut, maintaining accuracy becomes much more complicated, particularly when the angle of one end cut differs from the angle of the other end cut. Not only is the feed length of the material important, but also the angle at which the saw passes through the workpiece to cut the part. Miter saws typically have controls for adjusting this cutting angle and feed length. In the process of maintaining desired tolerances on feed length and cutting angle, variations in the material dimensions and location add complications. Stock material tolerances on metal workpieces may not be nearly accurate enough to be relied upon as a basis for making the cuts. That is, the cross-sectional dimensions and shapes can vary enough to affect the cut length. Warping and curvature along the length of the material can also affect the dimensions of the cut piece. Current miter saws have no automatic way of compensating for these problems and controlling the saw accordingly.
The problem is to adjust the cutting process so that stock with standard material tolerances may be utilized and produce parts to critical design dimensions. In the past, the main difficulty was that the feed lengths and cutting angles called for by the miter saw controller were fixed and necessarily based on nominal material dimensions and a fixed location of the material. Some improvements have been made by the operator measuring the actual dimensions of the workpiece and manually adjusting the saw controller to compensate. This process has had mixed results because of variation in location of the parts, such as described further herein, and the necessary but inaccurate assumption that the stock size is uniform along the entire length of the workpiece. Also, it has been necessary for the operator to edit the programming of the controller to compensate for the errors observed in earlier cuts. This practice can result in wasted material as well as time delays in production.
There is a need, therefore, for a control system for material cutting apparatus, such as a miter saw, which can actively measure the workpiece and use this information to compensate for these errors. This system would control the positioning of the workpiece and the cutting angle to obtain the desired tolerances in the final parts. The present invention meets this need by providing an active measurement and control system which determines variations in material displacement from a datum plane to proximate and distal surfaces of the workpiece, transmits this information to a central processing unit in the control system for the miter saw, and automatically adjusts the feed length of the workpiece and the cutting angle of a saw head of the saw to compensate for the variations. The problems caused by material location and variations are eliminated or minimized by measuring distal and proximate displacement dimensions of the material actively and automatically with distal and proximate displacement sensors. The feed lengths and cutting angles are then adjusted during the process to provide the necessary compensation in real time in order to maintain the important dimensional criteria of the finished parts. This eliminates the need for test parts and the intermediate program editing described above, and provides for continuous automatic adjustments as the distal and proximate displacements change.